1. Technical Field
The invention relates to caps, particularly to caps for covering a tube end.
2. Related Art
In civil or construction engineering, many tubes or pipes must be used. Usually, such piping engineering lasts a long period of time. Thus, installed pipelines will be polluted or choked up if they are not protected. To avoid this problem, an end of a tube is always provided with a cap.
On the other hand, before tube s or pipes have been installed, they must be transported, stored or processed. Within this period, the tubes or pipes are easy to be polluted by dust and moisture. The polluted tubes or pipes may become unavailable. Especially in some special usages, for example, ventilation pipes in a clean room, polluted pipes cannot be permitted to use.
It is effective that a tube end is covered by a cap. A conventional cap is provided with a thread to be screwed with a tube. FIG. 6 shows a disk-shaped cap for temporary protection. The cap has a disk body 9, which is plugged in a tube end 2 to prevent foreign matter from entering the tube. Such a cap uses tight fit between an outer cylindrical wall of the disk body 9 and an inner cylindrical wall of the tube end 2 to make a firm connection. The tight fit is formed by surface contact. Thus, considerable friction must be fought when the cap is being installed or removed. It is very laborious. Particularly, removing the cap is much more difficult than installing.
Additionally, the disk-type cap is made by the plastic injection molding process. The molds for plastic injection are very expensive, and thickness of the cap is hard to keep even. Thus the costs of the conventional cap are hard to be reduced. This is a real problem to be solved.